Constant pressure hydraulic power transmitting system



Feb. 10, 1953 E. v. BUNTING 2,627,815

CONSTANT PRESSURE HYDRAULIC POWER TRANSMITTING SYSTEM Filed Jan. 2, 1948Loan INVENTOR. ERNET l BUNT/NG BY:: 5 IWIAJ7J- A TTORNEY Patented Feb.10, 1953 UNITED STATES OFFICE CONSTANT PRESSURE HYDRAULICPOWEE-TRANSMITTING SYSTEM.

Ernest V. Bunting, Dearborn, Mich assignor to Harry Ferguson, Inc.,Detroit, Mich;, acorp'ora' tion of Delaware Application January 2, 1948,.SBIiaLNOi'ZZ'I" 7 Claims.

1 The present invention pertains to hydraulic power transmitting systemsand more particularly to. such systems of the constant pressure type;

One general object of the invention is to afford ahydraulic system inwhich fluid is pumped to build up a preselected fluid pressureandthereafter: maintained automatically at such value withonly such furtherpumping of fluid as is required for displacement of a load and tocompensatefor leakage, withdrawals to auxiliaries etc;

Ina: more specific aspect; it is an object to providea system of: suchcharacter in which the pumping is arrested simply by actuation ofv avalve mechanism and withoutentailing the constant spillage of fluid overa relietvalve or the complications of stoppage of the pump itself or ofvarying the pump stroke. By avoiding spillage through arelief valve theheating and foaming o1 thepressure fluid normally incident to suchoperation is obviated. By avoiding the complications of stoppage of thepump or variation-in its stroke, the cost of the system is reduced'an'dits reliability of operation enhanced.

Moreover, it is.an object to provide a system ofthe general characterindicated in whichthe pressure automatically retained can be variedmerely by' appropriate positioning of some manual-control device such asa hand lever or the like;

Further objects and: advantages of the iIlVEH tion will become apparentas the following description'proceeds; taken in connection withtheaccompanying drawings, in which:

Figure 1 is a diagrammatic layout of a con--- stant pressure'hydraulic'system embodying the present invention.

Fig: 2 is an enlarged longitudinal sectional view" of the controlvalve'included in the system of Fig. 1.

Fig; 3 is agenerally'diagrammatic layout of a suitablyadjustablemechanical linkage for inter connecting the pressureresponsive means and manual control with themain control valve of thesystem.

Variants in individual components of the sys'-'- tem will readilyoccurto skilled designers in this field. Accordingly, even though aparticular embodimentpfthe-invention has been indicated anddes'cri'bedin some detail, there. is 'no intention to thereby.limit'the'inventoin to such specific form of'employment'. Oh thecontrary, the intention isto cover allmodifications and' alternativearrangementsfa'lling within the spirit and. scope of the invention as.expressed in the appended claims.

Comprised in the system of Fig.1 is a main hydraulic actuator which maytake a variety of forms. Here-it is shown as a one-way ram l5,includinga cylinder l6 slidably receiving a piston ll. This. ram may bearranged to move some desired load" [8 applied to it. Pressure fluid;such as oil, is supplied to the ram l5'. from a sump 20 by a pump, 2 lthe latter being constantly.

driven by some suitablev power source (not.

shown). The-pump may b'e' of a simple, con.- stant displacement type.the discharge side of the pump ZI with the ram cylinder [6. Alsointerconnected'with the cylinder and pump-discharge is a drain line 23.

By blocking both the drain-linen and pump intake 24, fluid is trappedinthe system and, even thoughthe-pump continues to operate, no furtherfluid isdelivered byv it into the systems Opening the :pump. intake 24-while. retaining the drain 23 closed, permits the pump to deliveradditional fluid tothesystem Similarly, opening the drain 23-whileretaining the pump intakeZd closeddrains fluid from the. system,relieving.

pressure:in. .it. The: control. valve mechanism 25, one possiblezformofwhich islindicated in .Fig. 2, serves to effect-such blockingran'dopeningof the drain 23 and pump intake 24. 7

As shown in Fig. 2, the valve mechanism 25 may include a slidabl'eplunger 26 received in a bushingor'housing :21 having spaced. supplyports 28- and drain ports 29v- With the plunger. in its centralor-tneutral position as. shown,.both. the supply and-the: drain. ports.are. blocked, Movement of the plunger. in. one direction;. in thisinstance, tothe-left, fprogressivelysopens"the ports.

28 while retainingiportsi2 9.:closed.- Movementaof the plunger: in the.opposite direction effects H a similar progressive opening oflthe orts29 while. retaining ports 28. closed Return movementot the plunger to:neutral position progressively The tapers closes the open port or set"of 'ports'. formed on: the ends of: the: plunger"accentuatethe-progressive--character of its port opening: andclosingactions, and afiord more accurate-control with a minimum of overrun orthe pressure-adjustment in eitherdirectioni- The ports were ofcourse'connectedto the pump intake 24 while the drain. ports 29 areinterposed in thedrain or exhaust line-23. By-makingthe ports29 small,they constitute restricted orifices in the drain 'line therebyrestrainingtherateof descent of the ram piston.

It is with maintenance-of" preselected pressure A conduit 22"connects inthe system that the present invention is primarily concerned. It is withsuch end in view that a pressure responsive means or unit is connectedto the line 22 between pump and cylinder. Such means is showndiagrammatically in Fig. 1 as comprising a cylinder 3! having in it aslidable piston 32 whose movement is resisted by a compression spring33. Fluid led from the system into the cylinder 3| by a branch line 34urges the piston 32 to compress the spring 33. Displacement of thepiston 32 will therefore be substantially proportional to the pressureprevailing in the system.

Displacement of the piston 32 is utilized to shift the valve plunger 26.By providing between the pressure responsive means and valve amechanical connection 35 which is of selectively variable length-ratherthan a direct connection of constant lengthit is possible to vary atwill the system pressure at which the valv mechanism 25 is centered inits cut-off or neutral position. That is to say, each point in the pathof travel of the piston 32 corresponds to a different value of pressurein the system. And by making the connection between that piston and thevalve of suitable length the plunger can be. located in neutral for anygiven position (pressure setting) for the piston.

A suitable form of the linkage 35 for, in effect. Varying the length ofconnection noted is shown more or less diagrammatically in Fig. 3. Asthere indicated a connecting link 36 from the piston 32 is pivotallyconnected at 38 to the upper intermediate portion of a floating lever37. The lower end of this lever 3'! is pivotally connected to the valveplunger 26, whereas the upper end of the lever bears against a revolubleeccentric pin 33 on a hand lever 40 which is pivoted at 41. Acontractile spring '42 tends to rock the lever 37 clockwise about thepivot 38, retaining the lever in contact with the eccentric 39. Therange of movement of the hand control lever 43 between zero and maximumpressure positions is indicated in Fig. 3. Swinging the hand controllever 48 downward (to the left) rocks the lever 31 counterclockwiseabout the pivot 38, shortening the effective length L of the linkage.Conversely, pulling th hand lever 40 upward increases such efiectivelength. 7

Operation Let it be assumed initially that the handle or hand controllever 46 is pushed downward to its zero pressure position. In such casethe effective linkage length L is a minimum and the floating lever 37 isrocked counterclockwise, pulling the valve plunger 26 rightward so thatthe bleed ports 29 are uncovered, although supply ports 28 are blocked.In such condition fluid is bled from the system, relieving substantiallyall pressure.

To establishpressure in the system the operator has only to swing thehand control lever 48 upward. Thereupon the floating lever 37 is rockedclockwise about the pivot 38, pushing the valve plunger 26 leftward tocover the bleed ports 29 and open the supply ports 28. Delivery of oilto the system by the pump 2| ensues. As such delivery continues thesystem pressure rises, gradually forcing the piston 32 of the pressureresponsive means 33 inward against its spring That results in acorrespondinggradual rocking of the floating lever 3'1 in acounterclockwise direction, fulcruming in this instance about theeccentric 39 rather than about the pivot 33. The valve piston 23 isaccordingly shifted rightward, progressively closing and finallyblocking the intake ports 28. At such time the system is brought intoequilibrium with further delivery of fluid cut-oii.

The pressure prevailing in the system at outoff will depend upon theposition of the hand control lever 40. The higher that lever is in itsarc of travel, the longer the effective linkage length L. The largersuch length is, the farther must piston 32 be displaced to move thevalve plunger 25 to neutral. And each additional movement ofdisplacement for piston 32 requires an additional increment of fluidpressure on it.

Once cut-ofi or equilibrium condition is reached should the pressureinadvertently change for any reason, it is automatically restored to itspre-set value. Thus should the pressure go down, as because of leakagefor example, the pressure responsive devices piston 32 will creep to theleft, rocking the floating lever 37 clockwise to crack the supply ports28. The additional fluid so supplied quickly restores the system topressure and cut-off again takes place. Similarly should the pressurerise above the desired value, the resulting further displacement of thepiston 32 rocks the floating lever counterclockwise to open bleed ports29. As the pressure then falls cut-off occurs again when the pre-setpressure is reached.

To alter the pressure in the system at any time the operator has only tomake a corresponding change in the position of the hand lever 40. heshifts it the eccentric 39 is moved, displacing the lever 31 in adirection to bring about pumping or bleeding of fluid as the case may beand at the same time the effective linkage length L is changed toestablish a new cut-ofl point at the desired pressure value.

In building up to, and in retaining, a desired pressure in the system somuch fluid will be supplied as is required to meet the demands of themain ram l5 and of any auxiliaries which may be connected to the system,as for example, through a branch conduit 43 (Fig. 1). Additional fluidto move the ram piston l'i will, of course, be supplied only when itsload 18 is low enough to be overcome by the pressure for which thesystem is set. Exit of fluid from the pump discharge line 22 into eitherthe main ram IE or into an auxiliary tends, of course, to diminish thepressure in the system. Consequently, the valve mech anism is shiftedautomatically as previously described to admit fluid to the pump fordelivery into the system. Cut-off again occurs when the newlyestablished volume of fluid in the system is brought up to pressure.Should the pump delivery rate be high enough, as compared to the ratefluid is taken up, the actuator or the like being moved, the pump may becut-ofi" and reopened intermittently as the actuator operation proceeds.In any event, the system pressure is retained substantially constant atthe selected value. v

If desired a cut-oh" valve 44 may be interposed in the line 22 leadingto the ram I5. Closing that valve has the same effect as looking the rampiston against movement or imposing an immovable load on it. Pressurecan thus be built up to any desired value for the auxiliary line 43 withthe valve 44 closed and without regard to the actual load I8 on thepiston Ii.

From the foregoing it will be perceived that a constant pressurehydraulic system of rather remarkable structural simplicity and fidelityof opcan be of simple'form' requiring no stroke adjustmentsor the like.

ar'e' also structurally simple. Close fits and fine tolerances are notimperative. Complete freedom'of pressure adjustment is, however,attained, and the pressure fluid is fed by the pump when and only whenpressure requirements demaind iti I claim as my invention.

1. In a constant pressure type hydraulic system; the combination of apumphaving an intake'and a discharge, a drain connection leading fromthe pump discharge, a valve mechanism in-= eluding flow control meansshiftable from a neutral position in which both said pump intake anddrain connection are blocked into alternatively available exhaust andsupply positions in which said drain connection and intake arerespectively individually opened with the other remaining blocked, andmeans operable automatically in response to pump discharge pressure forretaining the flow control means of said valve mechanism in neutralposition so long as the prevailing discharge pressure is of apredetermined value and for correctively shifting said flow controlmeans to supply position or to exhaust position upon, respectively, adecrease or increase in discharge pressure from said predeterminedvalue.

2. In a constant pressure type hydraulic system, the combination of apump having an intake and a discharge, a drain connection leading fromthe pump discharge, a valve mechanism including flow control meansshiftable from a neutral position in which both said pump intake andsaid drain connection are blocked into alternatively available exhaustand supply positions in which said drain connection and intake arerespectively individually opened with the other remaining blocked, meansoperable automatically in response to pump discharge pressure forretaining the flow control means of said valve mechanism in neutralposition so long as the prevailing discharge pressure is of apredetermined value and for correctively shifting said flow controlmeans to supply position or to exhaust position upon, respectively, adecrease or increase in discharge pressure from said predeterminedvalue, and manually operable means for varying said predetermined valueof discharge pressure.

3. In a constant pressure type hydraulic system, the combination of apump having an intake and a discharge; a drain connection leading fromthe pump discharge; a valve mechanism including flow control meansshiftable from a neutral position, in which both said pump intake andsaid drain connection are blocked, into alternatively available exhaustand supply positions in which said drain connection and intake arerespectively individually opened with the other remaining blocked; apressure responsive device subjected to the pressure prevailing in saidpump discharge and including a shiftable element displaceable through afixed path of travel proportionately with changes in such pressure; amechanical operating connection from said element to the flow controlmeans of said valve mechanism; and a manual adjusting means forselectively varying the effective length of said operating connection.

4. In a constant pressure type hydraulic system, the combination of apump having an intake and a discharge, a valve mechanism includ- Thepressure responsive device 39 and adjustable connecting linkage 35 ingnow controlmeans" having alternatively" available supply and exhaustpositions forefe fecting, respectively, the supply of pressurefiu idfrom saidpumpand the exhaust of fluid through said discharge; a'pressure responsive'de-=- able elementof said pressure responsivedevice;- a connection from one endportionof said floa't ing lever to theflow control means of said-valve mechanism, and a manually positionablefulcrum for the other end portion of said lever for varying theeffective lever ratio between said shiftable f element and said valvemechanism.

5. In a constant pressure type: hydraulic system, the combination of apump having an intake and a discharge, a drain connection leading fromthe pump discharge, a valve mechanism having flow control meansshiftable from a neutral position in which both said pump intake andsaid drain connection are blocked into alternatively available exhaustand supply positions in which said drain connection and intake arerespectively individually opened with the other remaining blocked, apressure responsive device including a cylinder having a slidableposition therein subjected to the pressure prevailing at the dischargeof said pump, a spring for yieldably resisting displacement of saidpiston under the influence of said pressure, a floating lever, aconnecting means pivotally connected at one end to an intermediate pointon said lever and connected at the other end to said piston, aconnection from one end portion of said lever to the flow control meansof said valve mechanism, a fulcrum arranged to coact with the oppositeend portion of said lever, and manually operable means for shifting saidfulcrum to vary the relative lengths of the arms of said lever.

6. In a constant pressure type hydraulic system, the combination of apump having an intake and a discharge; a drain connection leading fromthe pump discharge; a valve mechanism including flow control meansshiftable from a neutral position, in which both said pump intake andsaid drain connection are blocked, gradually into alternativelyavailable exhaust and supply positions in which said drain connectionand intake are respectively individually opened progressively with theother remaining blocked, said flow control means in its return toneutral position progressively closing the open one of said intake andsaid drain connection; a pressure responsive device subjected to thepressure prevailing in said pump discharge and including a shiftableelement displaceable through a fixed path of travel proportionately withchanges in such pressure; a mechanical operating connection from saidelement to the flow control means of said valve mechanism; and a manualadjusting means for selectively varying the eflective length of saidoperating connection.

7. In a constant pressure type hydraulic system, the combination of apump having an intake and a discharge, a drain connection leading fromthe pump discharge, a valve mechanism including a flow control plungershiftable from a neutral position in which both said pump intake andsaid drain connection are blocked into alternatively available exhaustand supply posi- 7 tions in which said drain connection and intake arerespectively individually and progressively opened with the otherremaining blocked, said flow control plunger in its return to neutralposition progressively closing the open one of said intake and saiddrain connection, and means operable automatically in response to pumpdischarge pressure for retaining the flow control plunger of said valvemechanism in neutral posi-- tion so long as the prevailing dischargepressure is of a predetermined value and for correctively shifting saidflow control plunger to supply position or to exhaust position upon,respectively, a decrease or increase in discharge pressure from saidpredetermined value.

ERNEST V. BUNTING.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number 8 UNITED STATES PATENTS Name Date Drago Oct. 14, 1913 Staude Oct.16, 1923 Thiberge Aug. 22, 1933 Strum Mar. 27, 1934 Milotta July 31,1934 Gorsuch et al Sept. 25, 1934 Blume Jan. 15, 1935 Gifford Sept. 16,1941 Henke Jan. 4, 1944 Gregg Aug. 7, 1945 Pfost Mar. 19, 1946 Stokes eta1 July 1, 1947 Huber Dec. 23, 1947

